1. Field of the Invention
The present invention relates to self-adhesive labels and to a method of producing self-adhesive labels. In particular, the present invention relates to self-adhesive labels of multilaminar construction in which the label incorporates a booklet or folded sheet so as to provide a large surface area for carrying printed information which is greater than the surface area of the footprint of the label. The labels of the present invention have particular application in the labelling of pharmaceutical products.
2. Discussion of the Prior Art
A variety of so-called leaflet labels or booklet labels are known in the art and a typical label construction is disclosed in U.S. Pat. No. 5,399,403 in the name of David J. Instance. It is well known for the folded Leaflet or booklet to be overlaminated with a self-adhesive transparent plastics layer. The overlaminate provides durability to the label against inadvertent damage or tearing and also improves the aesthetic appearance of the label. Furthermore, the overlaminate can provide a structural part of the label to enable the leaflet or booklet label to be opened from a closed configuration by pulling the overlaminate away from a surface of a product, such as a pharmaceutical container, which is labelled to enable the leaflet or booklet to be read by a user. In some labels, the overlaminate can be re-adhered to the product to return the label to its closed configuration. Typical plastics materials for use as the overlaminate include oriented polypropylene carrying a pressure-sensitive adhesive on its rear surface.
U.S. Pat. No. 4,525,229 discloses a self-adhesive label in which an adhesive strip is provided to retain a folded strip in its folded configuration by being adhered to a top label and an underlying panel of the strip.
When pharmaceutical products are labelled, it is often necessary for the label to be printed with specific information, such as a lot of batch code and an expiry date. Such printing is generally achieved by providing a generic printed label for a particular pharmaceutical product and then overprinting a series of the labels with the required batch or lot code and expiry date.
A technical problem exists in the art in that there is a need to provide on overlaminated leaflet or booklet labels an area which is suitable for being printed with high quality alphanumeric printing devices suitable for printing batch codes, expiry dates and the like. There is also a need in the art for such overlarminated labels, particularly for pharmaceutical products, to be overprinted with bar codes which contain information relating to the overprinted batch codes, expiry dates, etc. and act as a security feature which can be scanned automatically to check that the required overprinting has been effected. The bar code needs to he small in area yet accurately printed in order to be machine readable at high speeds.
When information is overprinted onto paper, i.e. when a non-overlaminated leaflet or booklet label is being printed, ink is printed onto the paper surface of the label and then a laser is employed either to vaporise some of the ink so as to leave white lettering surrounded by the ink or to burn the lettering into the surface of the paper. The present inventor, has attempted to replicate this laser printing process onto a plastics overlaminate, in particular an oriented polypropylene self-adhesive laminate. However, following laser treatment the appearance of the printing is poor because the laminate tends to have a bubble effect imparted thereto by the laser, which the present inventor believes results from vapours being emitted from the paper surface and thermal distortion of the plastics laminate. In addition, it is believed that the overlarminate absorbs some of the energy from the laser which nay require the utilization of a relatively powerful laser, or a longer burn time, which may in turn exacerbate the bubbling problem,
The present inventor has also attempted to overprint onto a plastics overlaminate by using a thermal transfer printer. Such thermal transfer printers use a multi-element print head with a large number of tiny heating elements that can be turned on and off in a desired pattern or configuration under computer control so as to print selected alphanumeric characters. A ribbon is pressed between the print head and the substrate to be printed and when the print head elements are turned on so as to become heated, the elements soften the coating on the surface of the ribbon in contact with the substrate allowing the coating to stick to the substrate as a pattern of dots The desired alphanumeric symbols to be printed are of course controlled by selectively activating the desired pattern of heating elements. The present inventor has discovered that the plastics overlaminate surface tends not to be receptive to some thermal transfer coatings.
There is also a desire to overprint by means of wet printing. In wet printing a liquid vehicle of a wet printing ink dries by absorption into the printed substrate. This is not possible with a plastics overlaminate because the vehicle cannot absorb thereinto, leading to smudging of the printed image.
These problems have been solved in the prior art by adhering a self-adhesive overlabel to the upper surface of the overlaminate, which overlabel has an upper surface which can be printed on by at least one of laser printing and thermal transfer printing. Such a construction is disclosed in WO98/07133 in the name of David J Instance Limited. However, this solution necessarily results in increased material costs due to the need to provide extra material for the overlabel and increased production costs due to the need for an extra production step to apply the overlabel to the upper surface of the overlarminate.
WO 97/04433, WO98/07131 and WO98/07132 disclose other types of over-laminated leaflet labels,
It is therefore an object of the present invention to at least partially solve these problems of the prior art.